For typical needs, we recommend using the small network installer package mirrored throughout CTAN.
Specifically, download one of these files: install-tl.zip for Windows (6.8mb), or install-tl-unx.tar.gz (1.5mb) for everything else. (Although the .zip archive works fine on all platforms, the .tar.gz is smaller, since it omits installation support programs needed only on Windows. The two archives are otherwise identical.)
The above links use the generic mirror.ctan.org url which autoredirects to a CTAN mirror that should be reasonably nearby and reasonably up to date. However, perfect synchronization is not possible; if you have troubles following the links, your best bet is to choose one explicitly from the list of CTAN mirrors.
After unpacking the archive, move to the resulting install-tl-* subdirectory. Then follow the installation instructions or read the documentation.
If you need to download through proxies, use a ~/.wgetrc file with the proxy settings for wget. TeX Live always uses GNU wget to download.
Information about downloading/mirroring the TeX Live archive repository is available separately, as well as other ways to acquire TeX Live.